Plasma Nozzle Array for Providing Uniform Scalable Microwave Plasma Generation

ABSTRACT

The present invention provides microwave plasma nozzle array systems ( 10, 70, 230 , and  310 ) and methods for configuring microwave plasma nozzle arrays ( 37, 99 , and  337 ). The microwaves are transmitted to a microwave cavity ( 323 ) in a specific manner and form an interference pattern ( 66 ) that includes high-energy regions ( 69 ) within the microwave cavity ( 32 ). The high-energy regions ( 69 ) are controlled by the phases and the wavelengths of the microwaves. A plurality of nozzle elements ( 36 ) is provided in the array ( 37 ). Each of the nozzle elements ( 36 ) has a portion ( 116 ) partially disposed in the microwave cavity ( 32 ) and receives a gas for passing therethrough. The nozzle elements ( 36 ) receive microwave energy from one of the high-energy regions ( 69 ). Each of the nozzle elements ( 36 ) includes a rod-shaped conductor ( 114 ) having a tip ( 117 ) that focuses on the microwaves and a plasma ( 38 ) is then generated using the received gas.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to a concurrently filed PCT application Ser.No. ______, filed on Jul. 21, 2005, entitled “SYSTEM AND METHOD FORCONTROLLING A POWER DISTRIBUTION WITHIN A MICROWAVE CAVITY” which ishereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to plasma generating systems, and moreparticularly to microwave plasma systems having plasma nozzle arrays.

2. Discussion of the Related Art

In recent years, the progress on producing plasma has been increasing.Typically, plasma consists of positive charged ions, neutral species andelectrons. In general, plasmas may be subdivided into two categories:thermal equilibrium and thermal non-equilibrium plasmas. Thermalequilibrium implies that the temperature of all species includingpositive charged ions, neutral species, and electrons, is the same.

Plasmas may also be classified into local thermal equilibrium (LTE) andnon-LTE plasmas, where this subdivision is typically related to thepressure of the plasmas. The term “local thermal equilibrium (LTE)”refers to a thermodynamic state where the temperatures of all of theplasma species are the same in the localized areas in the plasma.

A high plasma pressure induces a large number of collisions per unittime interval in the plasma, leading to sufficient energy exchangebetween the species comprising the plasma, and this leads to an equaltemperature for the plasma species. A low plasma pressure, on the otherhand, may yield one or more temperatures for the plasma species due toinsufficient collisions between the species of the plasma.

In non-LTE, or simply non-thermal plasmas, the temperature of the ionsand the neutral species is usually less than 100° C., while thetemperature of electrons can be up to several tens of thousand degreesin Celsius. Therefore, non-LTE plasma may serve as highly reactive toolsfor powerful and also gentle applications without consuming a largeamount of energy. This “hot coolness” allows a variety of processingpossibilities and economic opportunities for various applications.Powerful applications include metal deposition systems and plasmacutters, and gentle applications include plasma surface cleaning systemsand plasma displays.

One of these applications is plasma sterilization, which uses plasma todestroy microbial life, including highly resistant bacterial endospores.Sterilization is a critical step in ensuring the safety of medical anddental devices, materials, and fabrics for final use. Existingsterilization methods used in hospitals and industries includeautoclaving, ethylene oxide gas (EtO), dry heat, and irradiation bygamma rays or electron beams. These technologies have a number ofproblems that must be dealt with and overcome and these include issuessuch as thermal sensitivity and destruction by heat, the formation oftoxic byproducts, the high cost of operation, and the inefficiencies inthe overall cycle duration. Consequently, healthcare agencies andindustries have long needed a sterilizing technique that could functionnear room temperature and with much shorter times without inducingstructural damage to a wide range of medical materials including variousheat sensitive electronic components and equipment.

Atmospheric pressure plasmas for sterilization, as in the case ofmaterial processing, offer a number of distinct advantages to users. Itscompact packaging makes it easily configurable, it eliminates the needfor highly priced vacuum chambers and pumping systems, it can beinstalled in a variety of environments without additional facilitationneeds, and its operating costs and maintenance requirements are minimal.In fact, the fundamental importance of atmospheric plasma sterilizationlies in its ability to sterilize heat-sensitive objects, simple-to-use,and faster turnaround cycle. Atmospheric plasma sterilization may beachieved by the direct effect of reactive neutrals, including atomicoxygen and hydroxyl radicals, and plasma generated UV light, all ofwhich can attack and inflict damage to bacteria cell membranes. Thus,there is a need for devices that can generate atmospheric pressureplasma as an effective and low-cost sterilization source.

One of the key factors that affect the efficiency of atmospheric plasmasterilization systems, as in the case of other plasma generatingsystems, is scalability of plasmas generated by the systems. There areseveral microwave nozzle based atmospheric pressure plasma systemswidely used in the industrial and educational institutions around theworld. The most of these designs are single nozzle based and they lacklarge volume scalability required for sterilization of medical devicesapplications. Also, such plasma systems generate high temperatureplasma, which is not suitable for sterilization applications.

One solution to provide uniform plasma uses a nozzle array coupled to amicrowave cavity. One of the challenging problems of such a system iscontrolling the microwave distribution within the microwave cavity sothat the microwave energy (or, equivalently microwave) is localized atintended regions (hereinafter, referred to as “high-energy regions”)that are stationary within the cavity. In such systems, plasmauniformity and scalability may be obtained by coupling nozzles to thecontrolled high-energy spots, which also enhances the operationalefficiency of the system.

Most of the conventional systems having a microwave cavity are designedto provide a uniform microwave energy distribution in the microwavecavity. For example, Gerling, “WAVEGUIDE COMPONENTS AND CONFIGURATIONSFOR OPTIMAL PERFORMANCE IN MICROWAVE HEATING SYSTEMS,” published onwww.2450mhz.com by Gerling Applied Engineering Inc. in 2000, teaches asystem having two rotating phase shifters. In this system, the tworotating phase shifters generate high-energy regions that continuouslymove within the microwave cavity to insure a uniform heatingdistribution within the microwave cavity.

In contrast to such conventional systems, a plasma generating systemthat has a plasma nozzle array should be able to deterministicallycontrol the microwave in its microwave cavity and generate high-energyregions coupled to the nozzle array. Thus, there is a strong need forplasma generating systems that can deterministically generate andcontrol high-energy regions within the microwave cavity and have plasmanozzle arrays disposed so as to receive microwave energy from thehigh-energy regions.

SUMMARY OF THE INVENTION

The present invention provides various systems that have microwaveplasma nozzle arrays and methods for configuring the plasma nozzlearrays.

According to one aspect of the present invention, a method forconfiguring a microwave plasma nozzle array includes steps of: directingmicrowaves into a microwave cavity in opposing directions such that themicrowaves interfere and form a standing microwave pattern that isstationary within the microwave cavity; adjusting a phase of at leastone of the microwaves to control high-energy regions generated by thestanding microwave pattern; and disposing a nozzle array at leastpartially in the microwave cavity so that one or more nozzle elements ofthe nozzle array are configured to receive microwave energy from acorresponding one of the high-energy regions.

According to another aspect of the present invention, a method forconfiguring a microwave plasma nozzle array includes steps of: directinga first pair of microwaves into a microwave cavity in opposingdirections along a first axis; directing a second pair of microwavesinto the microwave cavity in opposing directions along a second axis,the first axis being normal to the second axis such that the first andthe second pairs of microwaves interfere and form high-energy regionsthat are stationary within the microwave cavity; adjusting a phase of atleast one of the microwaves to control the high-energy regions; anddisposing a nozzle array at least partially in the microwave cavity sothat one or more nozzle elements of the nozzle array are configured toreceive microwave energy from a corresponding one of the high-energyregions.

According to still another aspect of the present invention, a microwaveplasma nozzle array unit includes: a microwave cavity; and an array ofnozzles, each of the nozzles including: a gas flow tube adapted todirect a flow of gas therethrough and having an inlet portion and anoutlet portion; a rod-shaped conductor axially disposed in the gas flowtube, the rod-shaped conductor having a portion disposed in themicrowave cavity to receive microwaves and a tip positioned adjacent theoutlet portion.

According to yet another aspect of the present invention, a microwaveplasma system includes: a microwave source; a pair of isolatorsoperatively connected to the microwave source; a microwave cavity havinga pair of inlets; a pair of waveguides, each of the waveguides beingoperatively connected to at least one of the isolators and to at leastone of the inlets of the microwave cavity; a pair of non-rotating phaseshifters, each of the non-rotating phase shifters being operativelyconnected to at least one of the waveguides and to at least one of theisolators; and an array of nozzles, each of the nozzles of the arrayincluding: a gas flow tube adapted to direct a flow of gas therethroughand having an inlet portion and an outlet portion; a rod-shapedconductor being axially disposed in the gas flow tube, the rod-shapedconductor having a portion disposed in the microwave cavity to receivemicrowaves and a tip positioned adjacent the outlet portion.

According to another aspect of the present invention, a microwave plasmasystem includes: a microwave source; an isolator operatively connectedto the microwave source; a microwave cavity having an inlet; a waveguideoperatively connected to the isolator and to the inlet of the microwavecavity; a non-rotating phase shifter operatively connected to thewaveguide and the isolator; a circulator operatively connected to thewaveguide and being configured to direct microwaves to the non-rotatingphase shifter; a sliding short circuit operatively connected to themicrowave cavity; and an array of nozzles, each of the nozzles of thearray including: a gas flow tube adapted to direct a flow of gastherethrough and having an inlet portion and an outlet portion; arod-shaped conductor being axially disposed in the gas flow tube, therod-shaped conductor having a portion disposed in the microwave cavityto receive microwaves and a tip positioned adjacent the outlet portion.

According to another aspect of the present invention, a microwave plasmasystem includes: a microwave source; a pair of isolators operativelyconnected to the microwave source; a microwave cavity having a pair ofinlets; a pair of waveguides, each of said waveguides being operativelyconnected to a corresponding one of said isolators and to acorresponding one of said inlets of the microwave cavity; a pair ofnon-rotating phase shifters, each of said non-rotating phase shiftersbeing operatively connected to a corresponding one of said waveguidesand to a corresponding one of said isolators; a pair of sliding shortcircuits, each of said sliding short circuits being operativelyconnected to said microwave cavity; and an array of nozzles, each of thenozzles of the array including: a gas flow tube adapted to direct a flowof gas therethrough and having an inlet portion and an outlet portion; arod-shaped conductor being axially disposed in the gas flow tube, therod-shaped conductor having a portion disposed in the microwave cavityto receive microwaves and a tip positioned adjacent the outlet portion.

According to another aspect of the present invention, a microwave plasmasystem, comprising: a microwave source; a microwave cavity having fourinlets; four waveguides, each of the waveguides being operativelyconnected to at least one of the inlets of the microwave cavity and themicrowave source; four non-rotating phase shifters, each of thenon-rotating phase shifters being operatively connected to at least oneof the waveguides and the microwave source; four circulators, each ofthe circulators being operatively connected to at least one of thewaveguides and being configured to direct microwaves generated by themicrowave source to at least one of the non-rotating phase shifters; andan array of nozzles, each of the nozzles of the array including: a gasflow tube adapted to direct a flow of gas therethrough and having aninlet portion and an outlet portion; and a rod-shaped conductor beingaxially disposed in the gas flow tube, the rod-shaped conductor having aportion disposed in the microwave cavity to receive microwaves and a tippositioned adjacent the outlet portion.

These and other advantages and features of the invention will becomeapparent to those persons skilled in the art upon reading the details ofthe invention as more fully described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a system having a plasma nozzle arrayin accordance with one embodiment of the present invention.

FIG. 2A schematically illustrates the interference of two microwaveswithin the microwave cavity of the system shown in FIG. 1, where themicrowaves travel in opposing directions.

FIG. 2B schematically shows a distribution of high-energy regions withinthe microwave cavity for the system shown in FIG. 1.

FIG. 3 is a schematic diagram of a system having a plasma nozzle arrayin accordance with another embodiment of the present invention.

FIG. 4A shows a top view of the microwave cavity and plasma nozzle arrayshown in FIG. 1.

FIG. 4B shows a cross-sectional view of the microwave cavity and nozzledepicted in FIG. 4A taken along the line IV-IV.

FIG. 4C shows a cross-sectional view of an alternative embodiment of themicrowave cavity and nozzle array depicted in FIG. 4B.

FIG. 4D shows a cross-sectional view of another alternative embodimentof the microwave cavity and nozzle array depicted in FIG. 4B.

FIG. 5A shows a top view of an alternative embodiment of the plasmanozzle array shown in FIG. 4A.

FIG. 5B shows a cross-sectional view of the microwave cavity and nozzlearray depicted in FIG. 5A taken along the line IV′-IV′.

FIG. 5C shows a cross-sectional view of an alternative embodiment of themicrowave cavity and nozzle array depicted in FIG. 5B.

FIG. 5D shows a cross-sectional view of another alternative embodimentof the microwave cavity and nozzle array depicted in FIG. 5B.

FIGS. 6A-6F show cross-sectional views of alternative embodiments of themicrowave plasma nozzle depicted in FIG. 4C, illustrating additionalcomponents for enhancing nozzle efficiency.

FIG. 7 is a schematic diagram of a system having a plasma nozzle arrayin accordance with another embodiment of the present invention.

FIG. 8 shows an interference pattern of high-energy regions found withinthe microwave cavity of the system shown in FIG. 7, illustrating onearrangement of the nozzle array in the high-energy regions.

FIG. 9 is a schematic diagram of a microwave cavity and waveguides forgenerating high-energy regions in a two-dimensional array form inaccordance with still another embodiment of the present invention.

FIG. 10 shows an alternative interference pattern of high-energy regionsfound within the microwave cavity of the systems shown in FIGS. 7 and 9,illustrating an alternative arrangement of the nozzle array in thehigh-energy regions.

FIG. 11 is a schematic diagram of a system having a plasma nozzle arrayin accordance with yet another embodiment of the present invention.

FIG. 12 shows a cross-sectional view of the microwave cavity and thenozzle array depicted in FIG. 11 taken along a direction normal to thez-axis.

FIG. 13 is an exploded perspective view of the nozzle shown in FIG. 12.

FIGS. 14A-14I show cross-sectional views of alternative embodiments ofthe rod-shaped conductor depicted in FIG. 13.

FIG. 15 shows a flowchart illustrating exemplary steps for coupling amicrowave nozzle array in accordance with at least one embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following detailed description is of the best currently contemplatedmodes of carrying out the invention. The description is not to be takenin a limiting sense, but is made merely for the purpose of illustratingthe general principles of the invention, since the scope of theinvention is best defined by the appended claims.

It must be noted that, as used herein and in the appended claims, thesingular forms “a”, “and”, and “the” include plural referents unless thecontext clearly dictates otherwise. Thus, for example, reference to “anozzle” includes one or more nozzles and equivalents thereof known tothose skilled in the art, and so forth.

As mentioned previously, conventional microwave plasma systems generatea uniform power distribution within a microwave cavity by controllingphase differences between two microwaves transmitted to the microwavecavity. Unlike existing systems, the present invention provides methodsand systems for controlling the phases of the microwaves so that theycan generate stationary high-energy regions within microwave cavities.Also methods for configuring a plasma nozzle array so as to use powerfrom the high-energy regions are disclosed.

FIG. 1 is a schematic diagram of a system 10 having a plasma nozzlearray in accordance with one embodiment of the present invention. Asillustrated, the system 10 comprises: a microwave source 13 having amicrowave power head 12 that generates microwaves and a power splitter14 having two outlets that split the microwaves generated by themicrowave power head 12; a pair of isolators 17 a and 17 b configured todissipate retrogressing microwaves that travel toward the microwavepower head 12, each isolator including a dummy load 18 a and 18 b fordissipating the retrogressing microwaves and a circulator 16 fordiverting the retrogressing microwaves to the corresponding dummy load18 a and 18 b; a pair of non-rotating phase shifters 24 a and 24 b forshifting the phases of the microwaves; a pair of circulators 22 a and 22b for directing microwaves from the power splitter 14 to thenon-rotating phase shifters 24 a and 24 b, respectively; waveguides 20 aand 20 b for transmitting microwaves; and a microwave cavity 32. In analternative embodiment, the system 10 may further comprise: couplers 26a and 26 b connected to power meters 28 a and 28 b for measuringmicrowave fluxes; and tuners 30 a and 30 b for matching impedance ofmicrowaves. Typically, the microwave power head 12 includes a microwavegenerator and a power supply, which are not shown in FIG. 1 forsimplicity. In another alternative embodiment, an isolator may belocated between the microwave power head 12 and the two-outlet powersplitter 14, thereby replacing the pair of isolators 17 a and 17 b.

A nozzle array 37 comprising one or more nozzles 36 is connected to themicrowave cavity 32 and generate plasma plumes 38 a to 38 n from a gasprovided from a gas tank 34 through a mass flow control (MFC) valve 35.Several embodiments of the nozzles 36 and the microwave cavity 32 thatmay be used for the system 10 are discussed in a copending PCTApplication entitled “Microwave Plasma Nozzle with Enhanced PlumeStability and Heating Efficiency,” filed on Jul. 5, 2005, which ishereby incorporated by reference in its entirety.

The microwaves 40 a and 40 b transmitted from the power splitter 14travel in opposing directions along an x-axis within the microwavecavity 32 and yield an interference pattern, as shown in FIG. 2A. FIG.2A shows a plot 50 of microwaves 52 a and 52 b that interfere with eachother to yield a standing microwave 54 within the microwave cavity 32.The abscissa and ordinate of the plot 50 represent the direction ofmicrowave propagations and amplitude of microwaves, respectively. Sincethe intensity of the standing microwave 54 is proportional to the squareof amplitude, the standing microwave 54 has peak locations 64 for eachcycle where the amplitude reaches its maximum amplitude 58. (Forsimplicity, hereinafter, the amplitude refers to the absolute value ofthe amplitude.)

High-energy regions 69 may refer to the locations where the amplitude ofthe standing microwave 54 exceeds a threshold 60 that may be set by auser. As will be explained in connection with FIGS. 5A and 10, more thanone nozzle may be located along x-direction in each high-energy region69. In such cases, the width 62 of the high-energy regions 69 may bedetermined considering the dimension of the nozzles, spacing between twoneighboring nozzles and the value of the maximum amplitude 58. Forexample, the user may set the threshold 60 to 75% of the maximumamplitude 58 to provide microwave energy for the entire nozzles in thehigh-energy regions 69.

Peak locations 64 and maximum amplitudes 58 of the peaks as well as awidth 62 of the high-energy regions 69 may be controlled by thenon-rotating phase shifters 24 a and 24 b, while a pitch 56 isdetermined by the wavelength of the microwaves 52 a and 52 b. If thephase difference between the microwaves 52 a and 52 b decreases, themaximum amplitude 58 and the width 62 of the high-energy regions 69increase. If the phases of two microwaves 52 a and 52 b are shifted inone direction along the x-axis, the peak locations 64 may shift in thatdirection.

FIG. 2B shows a distribution 66 of the high-energy regions 69 within themicrowave cavity 32 viewed in a direction normal to the x-z plane. Asshown in FIG. 2B, the high-energy regions 69 are generated byinterference of the microwaves 52 a and 52 b propagating in thedirections 68 a and 68 b, respectively, within the microwave cavity 32.As the microwaves 52 a and 52 b may be one-dimensional waves, each ofthe high-energy regions 69 may be in a rectangular strip shape andspaced by half of the pitch 56. In FIGS. 2A and 2B, the microwave cavityis assumed to be a rectangular parallelepiped for the purpose ofillustration. However, it should be apparent to those of ordinary skillin the art that the microwave cavity can have any other shape withoutdeviating from the present invention.

In an alternative embodiment, microwave source 13 may be replaced by twoseparate microwave power heads and two isolators attached thereto,respectively, where each microwave power head may transmit a microwaveto the microwave cavity 32. In this embodiment, two microwaves 52 a and52 b may have different wavelengths and amplitudes. However, by applyingthe same principle set forth above, the non-rotating phase shifters 24 aand 24 b can be used to control the peak locations 64 and the maximumamplitude 58 as well as the width 62 of high-energy regions 69.

FIG. 3 is a schematic diagram of a system 70 for deterministicallygenerating high-energy regions within a microwave cavity in accordancewith another embodiment of the present invention. As illustrated, thesystem 70 may include a microwave power head 72 for generatingmicrowaves; an isolator 74 having a dummy load 76 configured todissipate the retrogressing microwaves that propagate toward themicrowave power head 72 and a circulator 78 for diverting theretrogressing microwave to a dummy load 76; a non-rotating phase shifter82 for controlling a microwave phase; a circulator 80; a microwavecavity 92; a waveguide 90 for transmitting microwaves from the microwavepower head 72 to the microwave cavity 92; and a sliding short circuit 94for controlling the phase of the reflected microwaves. In an alternativeembodiment, the system 70 may further include a coupler 86 connected topower meters 84 for measuring microwave fluxes; and a tuner 88 formatching the impedance of the microwaves. In another alternativeembodiment, the sliding short circuit 94 may be replaced by a wall,where the dimensions of the microwave cavity 92 along the microwavepropagation is a multiple of half a wavelength of the microwaves. Anozzle array 99 comprising nozzles 98 may be connected to the microwavecavity 92 and generate plasma plumes 100 from a gas provided from a gastank 96. The specific details of the nozzles 98 will be discussed below.

In FIG. 3, an inset diagram 102 illustrates the propagation ofmicrowaves transmitted from the microwave power head 72 to the microwavecavity 92. The transmitted microwaves are reflected from the slidingshort circuit 94, as indicated by an arrow 104, and they interfere withthe incoming microwaves to generate standing microwaves within themicrowave cavity 92. The sliding short circuit 94 can control the phaseof the reflected microwaves and, if it is used in conjunction with anon-rotating phase shifter 82, control the locations and the maximumamplitude of the standing waves as well as the width of high-energyregions that are similar to the high-energy regions 69 shown in FIG. 2B.

FIG. 4A is a top view of the plasma nozzle array 37 shown in FIG. 1,illustrating the nozzles 36 located within the high-energy regions 69established within the microwave cavity 32 by microwaves traveling inopposing directions 68 a and 68 b. As illustrated, the nozzle arrayshown at 37 is described as a two-dimensional array. However, it shouldbe apparent to those of ordinary skill that other arrangements ofnozzles may be used. For example, the nozzle array 37 may have only aone-dimensional array of the nozzles 36 arranged in either thez-direction or the x-direction. It is noted that a nozzle array 99 inFIG. 3 may have the same arrangement as shown in FIG. 4A.

FIG. 4B shows a cross-sectional diagram 110 of the microwave cavity andnozzle array depicted in FIG. 4A taken along the direction IV-IV. Asillustrated, the microwave cavity 32 includes a wall 111 that forms agas flow channel 112 for admitting a gas from the gas tank 34; and acavity 113 for receiving microwaves transmitted from the microwavesource 13 and generating the high-energy regions 69. Each nozzle 36 mayinclude a gas flow tube 120 connected to the cavity wall 111 to receivea gas through the gas flow channel 112; a rod-shaped conductor 114having a portion 116 for collecting microwaves from the high-energyregions 69 in the cavity 113; and a vortex guide 118 disposed betweenthe rod-shaped conductor 114 and the gas flow tube 120. The vortex guide118 has at least one opening 119 for producing a helical swirl flow patharound the rod-shaped conductor 114. The microwaves received by therod-shaped conductor portion 116 are focused on its tapered tip 117 togenerate the plasma plumes 38 using the gas. The gas flow tube 120 maybe made of a material that is substantially transparent to microwaves.For example, the gas flow tube 120 may be made of a dielectric material,such as quartz.

The width 62 of the high-energy regions 69 may be optimized bycontrolling the non-rotating phase shifters 24 a and 24 b. In general, asmaller width of high-energy regions 69 may yield a higher operationalefficiency of the nozzles 36. However, considering the potentialvariation of the high-energy regions 69 during operation of the system10, the width 62 of the high-energy regions 69 may be slightly largerthan the diameter of the rod-shaped conductor 114.

FIG. 4C is a cross-sectional diagram of an alternative embodiment 122 ofthe microwave cavity and nozzle array depicted in FIG. 4B. Asillustrated, a nozzle 128 has similar components as those shown in FIG.4B. FIG. 4C includes a gas flow tube 134 sealingly connected to a wall126 to a receive a gas through a gas flow channel 127; a rod-shapedconductor 130 for collecting microwaves from the high-energy regions 69in a cavity 133; and a vortex guide 132. The gas flow tube 134 may bemade of any material that is substantially transparent to microwaves(i.e., microwaves can pass through the gas flow tube 134 with very lowloss of energy) and, as a consequence, the gas flowing through the gasflow tube 134 may be pre-heated within the cavity 133 prior to reachingthe region of the tapered tip of the rod-shaped conductor 130.

FIG. 4D shows a cross-sectional view of another alternative embodiment140 of the microwave cavity and nozzle array depicted in FIG. 4A. Asillustrated, nozzles 144 have components similar to their counterpartsin FIG. 4B: a gas flow tube 148 sealingly connected to a wall 143 of amicrowave cavity 142 to receive a gas; a rod-shaped conductor 152 forcollecting microwaves from the high-energy regions 69; and a vortexguide 146. The microwave cavity 142 may form a gas flow channelconnected to the gas tank 34. The rod-shaped conductor 152 may besimilar to the conductor 114 illustrated in FIG. 4B where the portion116 of the rod-shaped conductor 114 is inserted into the cavity 113 toreceive microwaves. Then, the received microwaves travel along thesurface thereof and are focused on the tapered tip.

A mentioned previously, the width 62 (FIG. 2) of the high-energy regions69 may be optimized by controlling the non-rotating phase shifters 24 aand 24 b. In general, a smaller width of high-energy regions 69 mayyield a higher operational efficiency of the nozzles 36. For thisreason, in FIGS. 4A-4D, the width 62 of the high-energy regions 69 maybe slightly larger than the diameter of the rod-shaped conductor 114. Inthese applications, the interval between two neighboring nozzles inx-direction may be half wavelength of the microwaves traveling inopposing directions 68 a and 68 b. However, in some applications, theinterval of half-wavelength may introduce fluctuations in plasmacharacteristics along the x-direction and, as a consequence, a smallerinterval between nozzles may be required. FIGS. 5A-5D illustrate nozzlearrays having various intervals between two neighboring nozzles inx-direction.

FIG. 5A is a top view of an alternative embodiment 37′ of the plasmanozzle array shown in FIG. 4A, illustrating nozzles 36′ located withinhigh-energy regions 69′ that are established by microwaves traveling inopposing directions 68 a′ and 68 b′. As depicted, the width 62′ of thehigh-energy region 69′ may be large enough to accommodate one or morenozzles 36′ in x-direction, even though the pitch 54′ is equal to thewavelength of the microwaves. The width 62′ may be controlled by varyingthe phase difference between the microwaves 68 a′ and 68 b′ as describedin connection with FIG. 2A. It is noted that a nozzle array 99 in FIG. 3may have the same arrangement as shown in FIG. 5A.

FIGS. 5B-5D are cross-sectional views of various embodiments of themicrowave cavity and nozzle array in FIG. 5A taken along the lineIV′-IV′. As illustrated, the three embodiments shown at 110′ (FIG. 5B),122′ (FIG. 5C) and 140′ (FIG. 5D) are similar to their counterpartsshown at 110, 122 and 140, respectively, with the difference that thewidth 62′ may be large enough to accommodate more than one nozzle inx-direction.

Each nozzle depicted in FIGS. 4B-4D and 5B-5D includes a rod-shapedconductor that has a portion inserted into the cavity to receivemicrowaves. Then, the received microwaves travel along the surfacethereof and are focused on the tapered tip. Since a portion of thetraveling microwaves may be lost through the gas flow tube, a shieldingmechanism may be used to enhance the efficiency of the nozzles, whichare illustrated in FIGS. 6A-6B.

FIG. 6A shows a cross-sectional view of a nozzle 160 which is analternative embodiment of the nozzle 36 shown in FIG. 4C. Asillustrated, the nozzle 160 includes: a rod-shaped conductor 162; a gasflow tube 164; a vortex guide 166; and an inner shield 168 for reducingmicrowave loss through the gas flow tube 164. The inner shield 168 has atubular shape and engages a recess formed along an outer surface of thevortex guide 166. The inner shield 168 may provide additional control ofthe helical swirl around the rod-shaped conductor 162 and increase theplasma stability by changing the gap between the gas flow tube 164 andthe rod-shaped conductor 162.

FIG. 6B is a cross-sectional view of another nozzle 170 which is anotheralternative embodiment of the nozzle 36 shown in FIG. 4C. Asillustrated, the nozzle 170 includes: a rod-shaped conductor 172; a gasflow tube 174; a vortex guide 176; and a grounded shield 178 forreducing microwave power loss through the gas flow tube 174. Thegrounded shield 178 may cover a portion of the gas flow tube 174 that isoutside of the microwave cavity. Like the inner shield 168, the groundedshield 178 may provide the additional control of the helical swirlaround the rod-shaped conductor 172 and increase the plasma stability bychanging the gap between the gas flow tube 174 and the rod-shapedconductor 172.

As mentioned above, the main heating mechanism applied to the nozzlesshown in FIGS. 4B-4D and 5B-5D are the microwaves that are focused anddischarged adjacent the tapered tip of the rod-shaped conductor, wherethe nozzles may produce non-LTE plasmas for sterilization. In non-LTEplasmas, the temperature of ions and neutral species may be less than100° C., while the temperature of electrons can be up to several tens ofthousand degrees in Celsius. Thus, such plasmas are highlyelectronically excited. To enhance the electronic temperature andincrease the nozzle efficiency, the nozzles may include additionalmechanisms that electronically excite the gas while the gas is withinthe gas flow tube, as illustrated in FIGS. 6C-6F.

FIG. 6C is a cross-sectional view of a nozzle 180 which is still anotheralternative embodiment of the nozzle 36 shown in FIG. 4C. Asillustrated, the nozzle 180 includes: a rod-shaped conductor 182; a gasflow tube 184; a vortex guide 186; and a pair of outer magnets 188 forelectronic excitation of the swirling gas in the gas flow tube 184. Eachof the outer magnets 188 may have a cylindrical shell having asemicircular cross section disposed around the outer surface of the gasflow tube 184.

FIG. 6D shows a cross-sectional view of a nozzle 190 which is yetanother alternative embodiment of the nozzle 36 shown in FIG. 4C. Asillustrated, the nozzle 190 includes: a rod-shaped conductor 192; a gasflow tube 194; a vortex guide 196; and a pair of inner magnets 198,secured by the vortex guide 196 within the gas flow tube 194, forelectronic excitation of the helical swirl in the gas flow tube 194.Each of the inner magnets 198 may have a cylindrical shell having asemicircular cross section.

FIG. 6E shows a cross-sectional view of a nozzle 200 which is a furtheralternative embodiment of the nozzle 36 shown in FIG. 4C. Asillustrated, the nozzle 200 includes: a rod-shaped conductor 202; a gasflow tube 204; a vortex guide 206; a pair of outer magnets 208; and aninner shield 210. Each of the outer magnets 208 may have a cylindricalshell having a semicircular cross section. In an alternative embodiment,the inner shield 210 may have a tubular shape.

FIG. 6F is a cross-sectional view of a nozzle 212 which is anotheralternative embodiment of the nozzle 36 shown in FIG. 4C. Asillustrated, the nozzle 212 includes: a rod-shaped conductor 214; a gasflow tube 216; a vortex guide 218; an anode 220; and a cathode 222. Theanode 220 and the cathode 222, connected to an electrical power source(not shown in FIG. 5F for simplicity), may electronically excite theswirling gas in the gas flow tube 216.

As mentioned above, FIGS. 6A-6F show cross-sectional views of variousembodiments of the nozzle 36 shown in FIG. 4B. However, it should beapparent to one of ordinary skill that the embodiments shown in FIGS.6A-6F can be applied to the nozzles shown in FIGS. 4C-4D and 5B-5D.Also, one skilled in the art will appreciate that the descriptions inFIGS. 4A-6F may be equally applied to the system 70 in FIG. 3.

Referring back to FIG. 2B, the nozzles 36 may be configured within thehigh-energy regions 69 to maximize the use of microwave energy withinthe microwave cavity 32. In general, operational efficiency of themicrowave cavity 32 may increase if the high-energy regions 69 areconfined only around the nozzles 36. As the cross section of a typicalnozzle is circular or rectangular with an aspect ratio of a near unity,operational efficiency of the microwave cavity may be maximized if thehigh-energy regions are confined within rectangular regions in a2-dimensional matrix form as will be described in FIGS. 7-9.

FIG. 7 is a schematic diagram of a system shown at 230 having a plasmanozzle array in accordance with one embodiment of the present invention.The components of the system shown at 230 are similar to theircounterparts of FIG. 1, except that the microwaves are traveling normalto each other in a microwave cavity 250. As illustrated, the system 230includes: a microwave source 233 that has a microwave power head 232 anda power splitter 234 having two outlets; a pair of non-rotating phaseshifters 244 a and 244 b; a pair of isolators 237 a and 237 b includinga pair of circulators 236 a and 236 b and a pair of dummy loads 238 aand 238 b; a pair of circulators 242 a and 242 b; waveguides 240 a and240 b; the microwave cavity 250; one or more nozzles 256, preferablyforming a two-dimensional array; and a pair of sliding short circuits254 a and 254 b. Inset diagrams 260 a and 260 b represent microwavestransmitted to the microwave cavity 250. The system 230 may furtherinclude: a pair of couplers 246 a and 246 b; a pair of tuners 248 a and248 b; and a pair of power meters 247 a and 247 b connected to a pair ofcouplers 246 a and 246 b, respectively. The gas tank 34 may be connectedto the microwave cavity 250 to provide a gas to the nozzles 256 that arecoupled to the microwave cavity 250. In an alternative embodiment, anisolator may be located between the microwave power head 232 and thepower splitter 234, replacing the isolators 237 a and 237 b.

FIG. 8 illustrates a distribution of high-energy regions within themicrowave cavity 250 viewed in a direction normal to a plane defined bythe propagation directions of two interfering microwaves, wherein thetwo microwaves are shown by waveforms 260 a and 260 b. As shown in FIG.8, two microwaves, shown by the waveforms 260 a and 260 b, and tworeflected microwaves, shown by waveforms 261 a and 261 b, generatehigh-energy regions 268 in a two-dimensional array form, where intervals264 a and 264 b correspond to half-wavelengths of the microwaves 260 aand 260 b, respectively. By the same principle as applied to theinterference pattern shown in FIG. 2B, the microwaves 260 a and 261 a,and the microwaves 260 b and 261 b, generate two standing microwavesthat yield strip-shaped high-energy regions 262 a and 262 b,respectively. Then, the standing microwaves may further interfere togenerate high-energy regions 268 in a matrix form as depicted in FIG. 8.Locations and widths 266 a and 266 b of the high-energy regions 258 maybe controlled by the non-rotating phase shifters 244 a and 244 b and/orthe sliding short circuits 254 a and 254 b. A portion of the rod-shapedconductor of each nozzle 256 may be located within the high-energyregions to collect the microwave energy, as illustrated in FIG. 8.

In an alternative embodiment, two separate microwave power heads mayreplace the microwave source 233, where each microwave power head maytransmit microwaves to the microwave cavity 250. In such embodiment, twomicrowaves may have different wavelengths and amplitudes, and as aconsequence, the intervals 264 a and 264 b may be different from eachother. Likewise, the widths 266 a and 266 b of the high-energy regionsmay be different from each other.

FIG. 9 is a schematic diagram of a microwave cavity and waveguides,collectively shown at 270, for generating high-energy regions in atwo-dimensional array form in accordance with still another embodimentof the present invention. As illustrated, a microwave cavity 276 mayreceive four microwaves 274 a to 274 d traveling through four waveguides272 a to 272 d, respectively. The phases of the microwaves may becontrolled by a corresponding one of four non-rotating phase shifters(not shown in FIG. 9) coupled to the waveguides 272 a to 272 d,respectively. The four microwaves 274 a to 274 d may be generated by oneor more microwave power heads. Each of four microwaves 274 a to 274 dmay be generated by a corresponding one of the four microwave powerheads, respectively. In an alternative embodiment, two microwave powerheads generate microwaves, where each microwave is split into twomicrowaves. In another alternative embodiment, one microwave power headmay be split into four microwaves using a power splitter having fouroutlets. It is noted that these three embodiments are provided forexemplary purposes only. Thus, it should be apparent to those ofordinary skill that any suitable system with the capability of providingfour microwaves may be used with the microwave waveguides 272 a to 272 dwithout deviating from the present invention.

Various embodiments of nozzles in FIGS. 6A-6F and walls of microwavecavities in FIG. 4B-4D that form gas flow channels may be also appliedto the systems described in FIG. 9. For simplicity, such embodimentshave not been shown.

Referring back to FIG. 8, the intervals 264 a and 264 b between twoneighboring nozzles in x- and z-directions may be half wavelengths ofthe microwaves shown by the waveforms 260 a and 260 b, respectively. Insome applications, these half-wavelength intervals may introducefluctuations in plasma characteristics along the x- and z-directionsand, as a consequence, smaller intervals may be required. For example,FIG. 10 schematically shows an alternative interference pattern of thehigh-energy regions found within the microwave cavity of the systemsdepicted in FIGS. 7 and 9. As illustrated, each high-energy region 268′may contain more than one nozzle 256′ providing smaller intervalsbetween neighboring nozzles. By reducing the intervals, the nozzle arraycoupled to the microwave cavity 250′ may be able to generate a plasmahaving an enhanced uniformity in both x- and z-directions. As in thecase of FIG. 8, the width 266 a′ of each high energy region 268′ may becontrolled by adjusting the phase difference between two microwaves 260a′ and 261 a′, while the width 266 b′ may be controlled by adjusting thephase difference between two microwaves 260 b′ and 261 b′.

FIG. 11 is a schematic diagram of a system shown at 310 and having aplasma nozzle array 337 in accordance with still another embodiment ofthe present invention. As illustrated, the system shown at 310 is quitesimilar to the system shown at 10 (FIG. 1) with the difference thatnozzles 336 in a nozzle array 337 may receive gas directly from a gastank 334. The gas line 370 from the gas tank 334 may have a plurality ofbranches 371, wherein each branch may be coupled to one of the nozzles336 and formed of a conventional gas tube.

FIG. 12 shows a cross-sectional view of the microwave cavity 332 andnozzle array 337 taken along a direction normal to the z-axis in FIG.11. As illustrated, a nozzle 336 may includes: a gas flow tube 358; agrounded shield 360 for reducing microwave loss through gas flow tube358 and sealed with the cavity wall 332, the gas flow tube 358 beingtightly fitted into the grounded shield 360; a rod-shaped conductor 352having a portion 354 disposed in the microwave cavity 332 for receivingmicrowaves from within the microwave cavity 332; a position holder 356disposed between the rod-shaped conductor 352 and the grounded shield360 and configured to securely hold the rod-shaped conductor 352relative to the ground shield 360; and a gas feeding mechanism 362 forcoupling the branch 371 to the grounded shield 360. The position holder356, grounded shield 360 and rod-shaped conductor 352 may be made of thesame materials as those of the vortex guide 146 (FIG. 4D), groundedshield 178 (FIG. 6B) and rod-shaped conductor 152 (FIG. 4D),respectively. For example, the grounded shield 360 may be made of metaland preferably copper.

As illustrated in FIG. 12, the nozzle 336 may receive gas through thegas feeding mechanism 362. The gas feeding mechanism 362 may be apneumatic one-touch fitting (model No. KQ2H05-32) made by SMCCorporation of America, Indianapolis, Ind. One end of the gas feedingmechanism 362 has a threaded bolt that mates with the female threadsformed on the edge of a hole 364 in the grounded shield 360 asillustrated in FIG. 13. It should be apparent to those of ordinary skillthat the present invention may be practiced with other suitable types ofgas feeding mechanisms. Several embodiments of the nozzles 336 and themicrowave cavity 332 that may be used for the system 310 are discussedin the previously referred PCT Application entitled “Microwave PlasmaNozzle with Enhanced Plume Stability and Heating Efficiency,” filed onJul. 7, 2005.

FIG. 13 is an exploded perspective view of the nozzle 336 shown in FIG.12. As illustrated, the rod-shaped conductor 352 and the grounded shield360 can engage the inner and outer perimeters of the position holder356, respectively. The rod-shaped conductor 352 may have a portion 354that acts as an antenna to collect microwaves from the microwave cavity332. The collected microwave may travel along the rod-shaped conductor352 and generate plasma 338 using the gas flowing through the gas flowtube 358. The term rod-shaped conductor is intended to cover conductorshaving various cross sections such as circular, oval, elliptical, or anoblong cross section, or any combinations thereof.

The microwaves may be collected by the portion 354 of the rod-shapedconductor 352 that extends into the microwave cavity 332. Thesemicrowaves travel down the rod-shaped conductor toward the tapered tip.More specifically, the microwaves are received by and travel along thesurface of the rod-shaped conductor 352. The depth of the skinresponsible for microwave penetration and migration is a function of themicrowave frequency and the conductor material. The microwavepenetration distance can be less than a millimeter. Thus, a rod-shapedconductor 400 of FIG. 14A having a hollow portion 401 is an alternativeembodiment for the rod-shaped conductor 352.

It is well known that some precious metals are good microwaveconductors. Thus, to reduce the unit price of the device withoutcompromising the performance of the rod-shaped conductor, the skin layerof the rod-shaped conductor can be made of precious metals that are goodmicrowave conductors while cheaper conducting materials can be used forinside of the core. FIG. 14B is a cross-sectional view of anotheralternative embodiment of a rod-shaped conductor, wherein a rod-shapedconductor 402 includes skin layer 406 made of a precious metal and acore layer 404 made of a cheaper conducting material.

FIG. 14C is a cross-sectional view of yet another alternative embodimentof the rod-shaped conductor, wherein a rod-shaped conductor 408 includesa conically-tapered tip 410. Other cross-sectional variations can alsobe used. For example, conically-tapered tip 410 may be eroded by plasmafaster than another portion of rod-conductor 408 and thus may need to bereplaced on a regular basis.

FIG. 14D is a cross-sectional view of another alternative embodiment ofthe rod-shaped conductor, wherein a rod-shaped conductor 412 has ablunt-tip 414 instead of a pointed tip to increase the lifetime thereof.

FIG. 14E is a cross-sectional view of another alternative embodiment ofthe rod-shaped conductor, wherein a rod-shaped conductor 416 has atapered section 418 secured to a cylindrical portion 420 by a suitablefastening mechanism 422 (in this case, the tapered section 418 can bescrewed into the cylindrical portion 420 using the screw end 422) foreasy and quick replacement thereof.

FIGS. 14F-14I show cross-sectional views of further alternativeembodiments of the rod-shaped conductor. As illustrated, rod-shapedconductors 421, 424, 428 and 434 are similar to their counterparts 352(FIG. 13), 400 (FIG. 14A), 402 (FIG. 14B) and 416 (FIG. 14E),respectively, with the difference that they have blunt tips for reducingthe erosion rate due to plasma. It is noted that the various embodimentsof rod-shaped conductor depicted in FIGS. 14A-14I can be used in anyembodiment of the nozzle described in FIGS. 1 and 3-13.

FIG. 15 shows a flowchart 500 illustrating exemplary steps forconfiguring a microwave plasma nozzle array in accordance with at leastone embodiment of the present invention. At step 502, the first pair ofmicrowaves is directed into a microwave cavity in opposing directionsalong a first axis. Next, at step 504, the second pair of microwaves isdirected into the microwave cavity in opposing directions along a secondaxis, where the first axis is normal to the second axis such that thefirst and the second pairs of microwaves interfere to yield high-energyregions that are stationary within the microwave cavity. Then, a phaseof at least one microwave selected from the first and second pair ofmicrowaves is adjusted to control the high-energy regions at step 506.Finally, at step 508, a nozzle array is coupled to the microwave cavity,where one or more nozzle elements of the nozzle array are configured tocollect the microwave energy from a corresponding one of the high-energyregions.

While the present invention has been described with a reference to thespecific embodiments thereof, it should be understood, of course, thatthe foregoing relates to preferred embodiments of the invention and thatmodifications may be made without departing from the spirit and thescope of the invention as set forth in the following claims.

In addition, many modifications may be made to adapt a particularsituation, systems, process, process step or steps, to the objective,the spirit and the scope of the present invention. All suchmodifications are intended to be within the scope of the claims appendedhereto.

1. A method for configuring a microwave plasma nozzle array, comprisingthe steps of: directing microwaves into a microwave cavity in opposingdirections such that the microwaves interfere and form a standingmicrowave pattern that is stationary within the microwave cavity;adjusting a phase of at least one of the microwaves to controlhigh-energy regions generated by the standing microwave pattern; anddisposing a nozzle array at least partially in the microwave cavity sothat one or more nozzle elements of the nozzle array are configured toreceive microwave energy from a corresponding one of the high-energyregions.
 2. A method as defined in claim 1, wherein said step ofdirecting microwaves includes the steps of: transmitting microwaves tothe microwave cavity; and reflecting microwaves using a sliding shortcircuit operatively connected to the microwave cavity.
 3. A method asdefined in claim 1, wherein said step of directing microwaves includesthe step of: transmitting microwaves generated by two microwave powerheads to the microwave cavity.
 4. A method for configuring a microwaveplasma nozzle array, comprising the steps of: directing a first pair ofmicrowaves into a microwave cavity in opposing directions along a firstaxis; directing a second pair of microwaves into the microwave cavity inopposing directions along a second axis, the first axis being normal tothe second axis such that the first and the second pairs of microwavesinterfere and form high-energy regions that are stationary within themicrowave cavity; adjusting a phase of at least one of the microwaves tocontrol the high-energy regions; and disposing a nozzle array at leastpartially in the microwave cavity so that one or more nozzle elements ofthe nozzle array are configured to receive microwave energy from acorresponding one of the high-energy regions.
 5. A method as defined inclaim 4, wherein said step of directing the first pair of microwavesincludes the steps of: transmitting microwaves to the microwave cavity;and reflecting microwaves using a sliding short circuit operativelyconnected the microwave cavity.
 6. A method as defined in claim 4,wherein said step of directing the first pair of microwaves includes thestep of: transmitting microwaves generated by two microwave power headsto the microwave cavity.
 7. A method as defined in claim 4, furthercomprising the steps of: generating the microwaves by a microwave powerhead; and providing a power splitter connected to the microwave powerhead.
 8. A method as defined in claim 4, wherein said step of adjustinga phase of at least one of the microwaves includes adjusting phases ofthe first pair of microwaves.
 9. A method as defined in claim 4, whereinsaid step of adjusting a phase of at least one of the microwavesincludes adjusting phases of the second pair of microwaves.
 10. A methodas defined in claim 4, wherein said step of adjusting a phase of atleast one of the microwaves includes adjusting phases of both the firstpair and the second pair of microwaves.
 11. A microwave plasma nozzlearray unit, comprising: a microwave cavity; and an array of nozzles,each of said nozzles including: a gas flow tube adapted to direct a gasflow therethrough and having an inlet portion and an outlet portion; anda rod-shaped conductor axially disposed in said gas flow tube, saidrod-shaped conductor having a portion disposed in said microwave cavityto receive microwaves and a tip positioned adjacent said outlet portion.12. A microwave plasma nozzle array unit as defined in claim 11, whereineach of said nozzles further includes: a vortex guide disposed betweensaid rod-shaped conductor and said gas flow tube, said vortex guidehaving at least one passage for imparting a helical shaped flowdirection around said rod-shaped conductor to a gas passing along saidat least one passage.
 13. A microwave plasma nozzle array unit asdefined in claim 12, wherein said microwave cavity includes a wall, saidwall of said microwave cavity forming a portion of a gas flow passageoperatively connected to the inlet portion of said gas flow tube.
 14. Amicrowave plasma nozzle array unit as defined in claim 11, wherein eachof said nozzles further includes: a shield disposed adjacent to aportion of said gas flow tube for reducing a microwave power lossthrough said gas flow tube, said shield being made of a conductingmaterial.
 15. A microwave plasma nozzle array unit as defined in claim11, wherein each of said nozzles further includes: a grounded shielddisposed on an exterior surface of said gas flow tube for reducing amicrowave power loss through said gas flow tube, said grounded shieldhaving a hole for receiving the gas flow therethrough.
 16. A microwaveplasma nozzle array unit as defined in claim 15, wherein each of saidnozzles further includes: a position holder disposed between saidrod-shaped conductor and said grounded shield for securely holding saidrod-shaped conductor relative to said grounded shield.
 17. A microwaveplasma nozzle array unit as defined in claim 11, wherein said gas flowtube is made of quartz.
 18. A microwave plasma nozzle array unit asdefined in claim 11, wherein each of said nozzles further includes apair of magnets disposed adjacent to said gas flow tube, said pair ofmagnets having a shape approximating a portion of a cylinder.
 19. Amicrowave plasma nozzle array unit as defined in claim 11, wherein eachof said nozzles further includes: an anode disposed adjacent to aportion of said gas flow tube; and a cathode disposed adjacent toanother portion of said gas flow tube.
 20. A microwave plasma nozzlearray unit as defined in claim 11, wherein said microwave cavityincludes: a microwave inlet; and a sliding short circuit configured toreflect microwaves transmitted through said microwave inlet.
 21. Amicrowave plasma nozzle array unit as defined in claim 11, wherein saidmicrowave cavity includes: two microwave inlets disposed in oppositesides of said microwave cavity.
 22. A microwave plasma nozzle array unitas defined in claim 11, wherein said microwave cavity includes: twomicrowave inlets disposed in sides of said microwave cavity which arenon-nal to each other; and two sliding short circuits configured toreflect microwaves received by said inlets.
 23. A microwave plasmanozzle array unit as defined in claim 11, wherein said microwave cavityincludes: a first pair of microwave inlets disposed in opposite sides ofsaid microwave cavity along a first axis; a second pair of microwaveinlets disposed in opposite sides of said microwave cavity along asecond axis, the second axis being substantially normal to the firstaxis.
 24. A microwave plasma nozzle array unit as defined in claim 11,wherein said microwave cavity is configured to generate a plurality ofstationary high-energy regions using microwaves directed thereto andwherein said portion of said rod-shaped conductor is disposed within thespace occupied by said stationary high-energy regions.
 25. A microwaveplasma system, comprising: a microwave source; a pair of isolatorsoperatively connected to said microwave source; a microwave cavityhaving a pair of inlets; a pair of waveguides, each of said waveguidesbeing operatively connected to a corresponding one of said isolators andto a corresponding one of said inlets of said microwave cavity; and apair of non-rotating phase shifters, each of said non-rotating phaseshifters being operatively connected to a corresponding one of saidwaveguides and to a corresponding one of said isolators; and an array ofnozzles, each of said nozzles including: a gas flow tube adapted todirect a gas flow therethrough and having an inlet portion and an outletportion; and a rod-shaped conductor axially disposed in said gas flowtube, said rod-shaped conductor having a portion disposed in saidmicrowave cavity to receive microwaves and a tip positioned adjacentsaid outlet portion.
 26. A microwave plasma system as defined in claim25, wherein each of said nozzles further includes: a vortex guidedisposed between said rod-shaped conductor and said gas flow tube, saidvortex guide having at least one passage for imparting a helical shapedflow direction around said rod-shaped conductor to a gas passing alongsaid at least one passage.
 27. A microwave plasma system as defined inclaim 26, wherein said microwave cavity includes a wall, said wall ofsaid microwave cavity forming a portion of a gas flow passageoperatively connected to the inlet portion of said gas flow tube.
 28. Amicrowave plasma system as defined in claim 25, wherein each of saidnozzles further includes: a shield disposed adjacent to a portion ofsaid gas flow tube for reducing a microwave power loss through said gasflow tube, said shield being made of a conducting material.
 29. Amicrowave plasma system as defined in claim 25, wherein each of saidnozzles further includes: a grounded shield disposed on an exteriorsurface of said gas flow tube for reducing a microwave power lossthrough said gas flow tube, said grounded shield having a hole forreceiving the gas flow therethrough.
 30. A microwave plasma system asdefined in claim 29, wherein each of said nozzles further includes: aposition holder disposed between said rod-shaped conductor and saidgrounded shield for securely holding said rod-shaped conductor relativeto said grounded shield.
 31. A microwave plasma system as defined inclaim 25, wherein said gas flow tube is made of quartz.
 32. A microwaveplasma system as defined in claim 25, wherein each of said nozzlesfurther includes a pair of magnets disposed adjacent to said gas flowtube, said pair of magnets having a shape approximating a portion of acylinder.
 33. A microwave plasma system as defined in claim 25, whereineach of said nozzles further includes: an anode disposed adjacent to aportion of said gas flow tube; and a cathode disposed adjacent toanother portion of said gas flow tube.
 34. A microwave plasma system asdefined in claim 25, wherein said microwave cavity is configured togenerate a plurality of stationary high-energy regions using microwavesdirected thereto and wherein said portion of said rod-shaped conductoris disposed within the space occupied by said stationary high-energyregions.
 35. A microwave plasma system as defined in claim 25, whereineach of said isolators includes: a circulator operatively connected toat least one of said waveguides; and a dummy load operatively connectedto said circulator.
 36. A microwave plasma system as defined in claim25, further comprising: a pair of tuners, each of said tuners beingoperatively connected to a corresponding one of said waveguides and saidmicrowave cavity.
 37. A microwave plasma system as defined in claim 25,further comprising: a pair of circulators, each of said circulatorsbeing operatively connected to a corresponding one of said waveguidesand configured to direct microwaves to a corresponding one of saidnon-rotating phase shifters.
 38. A microwave plasma system as defined inclaim 25, further comprising: a pair of couplers, each of said couplersbeing operatively connected to a corresponding one of said waveguidesand a power meter for measuring microwave fluxes.
 39. A microwave plasmasystem as defined in claim 25, wherein said microwave source includes apair of microwave power heads, each of said microwave power heads beingoperatively connected to a corresponding one of said isolators.
 40. Amicrowave plasma system as defined in claim 25, wherein said microwavesource includes: a microwave power head for generating microwaves; and apower splitter for receiving, bisecting and directing the microwaves tosaid isolators.
 41. A microwave plasma system, comprising: a microwavesource; an isolator operatively connected to said microwave source; amicrowave cavity having an inlet; a waveguide operatively connected tosaid isolator and to said inlet of said microwave cavity; a non-rotatingphase shifter operatively connected to said waveguide and said isolator;a circulator operatively connected to said waveguide and configured todirect microwaves to said non-rotating phase shifter; a sliding shortcircuit operatively connected to said microwave cavity; and an array ofnozzles, each of said nozzles including: a gas flow tube adapted todirect a gas flow therethrough and having an inlet portion and an outletportion; and a rod-shaped conductor axially disposed in said gas flowtube, said rod-shaped conductor having a portion disposed in saidmicrowave cavity to receive microwaves and a tip positioned adjacentsaid outlet portion.
 42. A microwave plasma system as defined in claim41, wherein each of said nozzles further includes: a vortex guidedisposed between said rod-shaped conductor and said gas flow tube, saidvortex guide having at least one passage for imparting a helical shapedflow direction around said rod-shaped conductor to a gas passing alongsaid at least one passage.
 43. A microwave plasma system as defined inclaim 42, wherein said microwave cavity includes a wall, said wall ofsaid microwave cavity forming a portion of a gas flow passageoperatively connected to the inlet portion of said gas flow tube.
 44. Amicrowave plasma system as defined in claim 41, wherein each of saidnozzles further includes: a shield disposed adjacent to a portion ofsaid gas flow tube for reducing a microwave power loss through said gasflow tube, said shield being made of a conducting material.
 45. Amicrowave plasma system as defined in claim 41, wherein each of saidnozzles further includes: a grounded shield disposed on an exteriorsurface of said gas flow tube for reducing a microwave power lossthrough said gas flow tube, said grounded shield having a hole forreceiving the gas flow therethrough.
 46. A microwave plasma system asdefined in claim 45, wherein each of said nozzles further includes: aposition holder disposed between said rod-shaped conductor and saidgrounded shield for securely holding said rod-shaped conductor relativeto said grounded shield.
 47. A microwave plasma system as defined inclaim 41, wherein said gas flow tube is made of quartz.
 48. A microwaveplasma system as defined in claim 41, wherein each of said nozzlesfurther includes a pair of magnets disposed adjacent to said gas flowtube, said pair of magnets having a shape approximating a portion of acylinder.
 49. A microwave plasma system as defined in claim 41, whereineach of said nozzles further includes: an anode disposed adjacent to aportion of said gas flow tube; and a cathode disposed adjacent toanother portion of said gas flow tube.
 50. A microwave plasma system asdefined in claim 41, wherein said microwave cavity is configured togenerate a plurality of stationary high-energy regions using microwavesdirected thereto and wherein said portion of said rod-shaped conductoris disposed within the space occupied by said stationary high-energyregions.
 51. A microwave plasma system as defined in claim 41, whereinsaid isolator includes: a circulator operatively connected to saidwaveguide; and a dummy load operatively connected to said circulator.52. A microwave plasma system as defined in claim 41, furthercomprising: a tuner operatively connected to said waveguide and saidmicrowave cavity.
 53. A microwave plasma system as defined in claim 41,further comprising: a coupler operatively connected to said waveguideand a power meter for measuring microwave fluxes.
 54. A microwave plasmasystem, comprising: a microwave source; a pair of isolators operativelyconnected to said microwave source; a microwave cavity having a pair ofinlets; a pair of waveguides, each of said waveguides being operativelyconnected to a corresponding one of said isolators and to acorresponding one of said inlets of said microwave cavity; a pair ofnon-rotating phase shifters, each of said non-rotating phase shiftersbeing operatively connected to a corresponding one of said waveguidesand to a corresponding one of said isolators; a pair of sliding shortcircuits, each of said sliding short circuits being operativelyconnected to said microwave cavity; and an array of nozzles, each ofsaid nozzles including: a gas flow tube adapted to direct a gas flowtherethrough and having an inlet portion and an outlet portion; and arod-shaped conductor axially disposed in said gas flow tube, saidrod-shaped conductor having a portion disposed in said microwave cavityto receive microwaves and a tip positioned adjacent said outlet portion.55. A microwave plasma system as defined in claim 54, wherein each ofsaid nozzles further includes: a vortex guide disposed between saidrod-shaped conductor and said gas flow tube, said vortex guide having atleast one passage for imparting a helical shaped flow direction aroundsaid rod-shaped conductor to a gas passing along said at least onepassage.
 56. A microwave plasma system as defined in claim 55, whereinsaid microwave cavity includes a wall, said wall of said microwavecavity forming a portion of a gas flow passage operatively connected tothe inlet portion of said gas flow tube.
 57. A microwave plasma systemas defined in claim 54, wherein each of said nozzles further includes: ashield disposed adjacent to a portion of said gas flow tube for reducinga microwave power loss through said gas flow tube, said shield beingmade of a conducting material.
 58. A microwave plasma system as definedin claim 54, wherein each of said nozzles further includes: a groundedshield disposed on an exterior surface of said gas flow tube forreducing a microwave power loss through said gas flow tube, saidgrounded shield having a hole for receiving the gas flow therethrough.59. A microwave plasma system as defined in claim 58, wherein each ofsaid nozzles further includes: a position holder disposed between saidrod-shaped conductor and said grounded shield for securely holding saidrod-shaped conductor relative to said grounded shield.
 60. A microwaveplasma system as defined in claim 54, wherein said gas flow tube is madeof quartz.
 61. A microwave plasma system as defined in claim 54, whereineach of said nozzles further includes a pair of magnets disposedadjacent to said gas flow tube, said pair of magnets having a shapeapproximating a portion of a cylinder.
 62. A microwave plasma system asdefined in claim 54, wherein each of said nozzles further includes: ananode disposed adjacent to a portion of said gas flow tube; and acathode disposed adjacent to another portion of said gas flow tube. 63.A microwave plasma system as defined in claim 54, wherein said microwavecavity is configured to generate a plurality of stationary high-energyregions using microwaves directed thereto and wherein said portion ofsaid rod-shaped conductor is disposed within the space occupied by saidstationary high-energy regions.
 64. A microwave plasma system as definedin claim 54, wherein each of said isolators includes: a circulatoroperatively connected to at least one of said waveguides; and a dummyload operatively connected to said circulator.
 65. A microwave plasmasystem as defined in claim 54, further comprising: a pair of tuners,each of said tuners being operatively connected to a corresponding oneof said waveguides and said microwave cavity.
 66. A microwave plasmasystem as defined in claim 54, further comprising: a pair of couplers,each of said couplers being operatively connected to a corresponding oneof said waveguides and a power meter for measuring microwave fluxes. 67.A microwave plasma system as defined in claim 54, further comprising: apair of circulators, each of said circulators being operativelyconnected to a corresponding one of said waveguides and configured todirect microwaves to a corresponding one of said non-rotating phaseshifters.
 68. A microwave plasma system, comprising: a microwave source;a microwave cavity having four inlets; four waveguides, each of saidwaveguides being operatively connected to a corresponding one of saidinlets of said microwave cavity and said microwave source; fournon-rotating phase shifters, each of said non-rotating phase shiftersbeing operatively connected to a corresponding one of said waveguidesand said microwave source; four circulators, each of said circulatorsbeing operatively connected to a corresponding one of said waveguidesand configured to direct microwaves generated by said microwave sourceto at least one of said non-rotating phase shifters; and an array ofnozzles, each of said nozzles including: a gas flow tube adapted todirect a gas flow therethrough and having an inlet portion and an outletportion; and a rod-shaped conductor axially disposed in said gas flowtube, said rod-shaped conductor having a portion disposed in saidmicrowave cavity to receive microwaves and a tip positioned adjacentsaid outlet portion.
 69. A microwave plasma system as defined in claim68, wherein each of said nozzles further includes: a vortex guidedisposed between said rod-shaped conductor and said gas flow tube, saidvortex guide having at least one passage for imparting a helical shapedflow direction around said rod-shaped conductor to a gas passing alongsaid at least one passage.
 70. A microwave plasma system as defined inclaim 69, wherein said microwave cavity includes a wall, said wall ofsaid microwave cavity forming a portion of a gas flow passageoperatively connected to the inlet portion of said gas flow tube.
 71. Amicrowave plasma system as defined in claim 68, wherein each of saidnozzles further includes: a shield disposed adjacent to a portion ofsaid gas flow tube for reducing a microwave power loss through said gasflow tube, said shield being made of a conducting material.
 72. Amicrowave plasma system as defined in claim 68, wherein each of saidnozzles further includes: a grounded shield disposed on an exteriorsurface of said gas flow tube for reducing a microwave power lossthrough said gas flow tube, said grounded shield having a hole forreceiving the gas flow therethrough.
 73. A microwave plasma system asdefined in claim 72, wherein each of said nozzles further includes: aposition holder disposed between said rod-shaped conductor and saidgrounded shield for securely holding said rod-shaped conductor relativeto said grounded shield.
 74. A microwave plasma system as defined inclaim 68, wherein said gas flow tube is made of quartz.
 75. A microwaveplasma system as defined in claim 68, wherein each of said nozzlesfurther includes a pair of magnets disposed adjacent to said gas flowtube, said pair of magnets having a shape approximating a portion of acylinder.
 76. A microwave plasma system as defined in claim 68, whereineach of said nozzles further includes: an anode disposed adjacent to aportion of said gas flow tube; and a cathode disposed adjacent toanother portion of said gas flow tube.
 77. A microwave plasma system asdefined in claim 68, wherein said microwave cavity is configured togenerate a plurality of stationary high-energy regions using microwavesdirected thereto and wherein said portion of said rod-shaped conductoris disposed within the space occupied by said stationary high-energyregions.
 78. A microwave plasma system as defined in claim 68, whereinsaid microwave source includes: four microwave power heads; and fourisolators, each of said isolators being operatively connected to acorresponding one of said microwave power heads and to at least one ofsaid waveguides, each of said isolators including: a circulatoroperatively connected to said waveguide; and a dummy load operativelyconnected to said circulator.
 79. A microwave plasma system as definedin claim 68, wherein said microwave source includes: two microwave powerheads; two isolators, each of said isolators being connected to acorresponding one of said microwave power heads, each of said isolatorsincluding: a circulator operatively connected to said waveguide; and adummy load operatively connected to said circulator; and two powersplitters, each of said power splitters being operatively connected to acorresponding one of said isolators, each of said power splitters beingconfigured for receiving, bisecting and directing the microwaves to acorresponding two of said waveguides.
 80. A microwave plasma system asdefined in claim 68, wherein said microwave source includes: a microwavepower head; an isolator operatively connected to said microwave powerhead, said isolator including: a circulator operatively connected tosaid waveguide; and a dummy load operatively connected to saidcirculator; and a power splitter connected to said isolator, said powersplitter being configured to receive, split and direct the microwaves toa corresponding one of said waveguides.
 81. A microwave plasma system asdefined in claim 68, further comprising: four tuners, each of saidtuners being operatively connected to a corresponding one of saidwaveguides and said microwave cavity.
 82. A microwave plasma system asdefined in claim 68, further comprising: four couplers, each of saidcouplers being operatively connected to a corresponding one of saidwaveguides and a power meter for measuring microwave fluxes.